1. Field of the Invention
This invention relates generally to door latch mechanisms and, more particularly, to an outside thumb-piece door latch mechanism which has ergonomic features, is modular and can be used with any escutcheon, can be used with all type locks and which in the locked door mode provides greater resistance to abusive attack of the door latch mechanism and makes the thumb-piece and latch mechanism more durable and less susceptible to vandalism.
2. Description of Related Art
A common way to withdraw the latch bolt of a locked door is by rotation of a knob which when turned translates the rotational motion into linear motion for retracting or extending the door latch bolt from the door frame.
For some doors it is preferred to use a door handle in conjunction with a thumb-piece for pulling back the latch bolt from engagement with the frame before the door can be pulled open. The thumb-piece is typically of the pivot type which is stressful on the user's thumb when operating the door mechanism. In the instant invention the thumb piece may be moved linearly up and down and the linear motion is translated into a transverse back and forth horizontal linear motion for withdrawing the latch bolt from the door frame. The latch bolt is normally extended into the door frame. The linear up and down motion of the thumb-piece provides a mechanism which is ergonomic, i.e., less stressful on the user.
Thumb-piece actuators are well known in the art and it is a problem that in the locked door mode (the door latch bolt cannot be retracted) a person trying to open the door may subject the thumb-piece to abusive attack such as banging which can lead to damaging the door locking mechanism. This is particularly a problem with regard to vandalism or to an illegal entry through the door and it is necessary to provide an improved thumb-piece door latch mechanism which is more resistant to abusive attack, durable, and less susceptible to vandalism.
Door handles with thumb pieces are numerous and extremely varied and most are complex and commonly need numerous parts increasing the number of factory operations and complicating the positioning of parts in the structure. Gear action has been resorted to but is an expensive construction. Other mechanical devices using shafts, levers, cams, and bell cranks also take up considerable space and require relatively large and bulky housing thereby adding to the initial cost and increased installation costs.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a door latch mechanism which uses a thumb-piece to extend and retract a door latch from a door frame, which mechanism is of a design having ergonomic features, is modular, of simple construction and provides enhanced resistance to abusive attack making the mechanism durable and less susceptible to vandalism. For convenience the following description will be directed to a thumb piece which moves linearly up and down but it will be appreciated to those skilled in the art that a pivoted thumb piece may also be used where an ergonomic design is not desired.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.